New Materials Could Turn Near-Fantastic Devices like Invisibility Cloaks and Hyperlenses into Reality
Alexandra Boltasseva1 and Harry A. Atwater2
1: School of Electrical & Computer Engineering and Birck Nanotechnology Center, Purdue University, IN, USA.
2: Applied Physics and Kavli Nanoscience Institute, California Institute of Technology, USA.
We have started a new research direction of developing new classes of materials that could serve as building blocks for advanced nanophotonic devices based on a novel concept of metamaterials, ranging from powerful nanoscale-resolution microscopes and improved solar cells to invisibility cloaks and new quantum optics devices.
Harry A. Atwater
We are now entering a new age of Metamaterials (MMs). These are artificial, engineered materials can be tailored for almost any application due to their extraordinary response to electromagnetic, acoustic and thermal waves that transcend the properties of “natural” materials. The astonishing MM-based designs and near-fantastic predictions by a new field of transformation optics range from a negative index of refraction, focusing and imaging with nanoscale resolution, invisibility cloaks and optical black holes to nanoscale optics and advanced quantum information applications.
Past 2Physics articles based on works of Harry A. Atwater:
May 02, 2010: "A Versatile Negative Index Metamaterial Design for Visible Light" by Stanley P. Burgos and Harry A. Atwater
March 26, 2007: "Negative Refraction of Visible Light"
We recently realized that metals like silver and gold that have traditionally been the material of choice for making MMs but suffer from high losses at operational frequencies (the visible or the near-infrared (NIR) ranges) could be successfully replaced by other materials . Such development and optimization of materials has traditionally played a very important role in the development of new technologies. Similar to the infancy years of nanoelectronics, where the properties of silicon were rather poor, nanophotonics required another look at its fundamental building blocks - a step that is now marked by the recent Science article .
Material space for plasmonics and metamaterial applications: The important material parameters such as carrier concentration (maximum doping concentration for semiconductors), carrier mobility and interband losses form the optimization phase space for various applications. While spherical bubbles represent materials with low interband losses, elliptical bubbles represent those with larger interband losses in the corresponding part of the electromagnetic spectrum .
Now, we are working on replacing silver and gold by new materials that can be created using two options: making semiconductors more metallic by doping (like transparent conducting oxides) or making metal ‘less metallic’ by adding non-metallic elements (like titanium nitride, which looks like gold but has better properties). When these new materials are used for making MM and transformation optics devices (for example, "hyperlens" that provides nanoscale resolution not achievable with conventional optics), they outperform devices made with silver and gold .
Researchers are developing a new class of "plasmonic metamaterials" as potential building blocks for advanced optical technologies and a range of potential breakthroughs in the field of transformation optics. This image shows the transformation optics "quality factor" for several plasmonic materials: Gallium and Aluminum-doped zinc oxide (GZO, AZO), indium tin oxide and silver. For transformation optical devices, the quality factor rises as the amount of light "lost" or absorbed by plasmonic materials falls, resulting in materials that are promising for a range of advanced technologies. (Birck Nanotechnology Center, Purdue University)
New materials could turn many other MM designs and ideas into real-life devices: novel nano-patterning techniques capable of creating nanoscale features using light, advanced sensors and new types of light-harvesting systems for more efficient solar cells, a cloak of invisibility and new generation of quantum optical devices.
This work was supported by ONR-MURI grant N00014-10-1-0942 (AB) and U.S. Department of Energy grant DOE DE-FG02-07ER46405 and AFOSR grant FA9550-09 1 0673 (HAA).
 A. Boltasseva and H. A. Atwater, "Low-loss plasmonic metamaterials," Science 331, 290-291 (2011). Abstract.
 G. Naik and A. Boltasseva, "Semiconductors for plasmonics and metamaterials," Physica Status Solidi RRL 4, 295-297 (2010). Abstract.